This invention relates to power switching or transmission apparatus of an outboard engine, and more particularly to power switching apparatus of an outboard engine capable of improving the follow up characteristic and the operating feeling of the switching mechanism at the time of switching the power.
As shown in FIG. 5, in a prior art switching mechanism utilized to switch a forward rotation condition (forward advance), a reverse rotation condition (rearward advance) and a neutral condition of a propeller, a shift cam 2 is moved by the vertical or axial operation of a shift rod 1 to select one of the forward position F, neutral position N and reverse position R formed on the surface of the cam 2. The shift cam 2 moves a shifter dog 6 through a dog pin 5 by pushing a push rod 3 or the shifter dog 6 returns to the neutral position by the force of a return spring 4 so as to cause the dog 6a of the shifter dog 6 to engage with the dogs 7a or 8a of a forward gear 7 or a reverse gear 8, or to cause the dog to assume the neutral position in which the dog 6a does not engage with the dogs 7a and 8a. When dog 6a engages with one of the dogs 7a and 8a of gears 7 and 8, the drive shaft 9 rotates a propeller shaft 10 in the forward or reverse direction through the gear 7 or 8.
In the power switching mechanism of the prior art outboard engine having a construction as above discribed, there is a defect that as the shift cam 2 is moved from the neutral position N to the reverse position R to cause the shifter dog 6 to engage with the reverse gear 8, if the operating speed of the shift cam 2 is low, the corner portions of the dogs 6a and 8a are subjected to an impact force when engagement of the shifter dog 6 and the reverse gear 8 is shallow whereby these portions are worn to decrease the operating feeling.
There is another defect that when the shift cam 2 is brought to the neutral or forward position, as the number of revolution of the engine is increased while the shift cam 2 is being set at the reverse position, the shifter dog 6 would be moved to the neutral position or the forward position by the force of the return spring 4, but at this time since the contact pressure caused by the engagement of the shifter dog 6 and the dog 8a of the reverse gear 8 is high, there arises a case wherein the force of the return spring 4 can not move the shifter dog 6. For this reason, the mechanism has been constructed such that the angle of engagement between dogs 6a and 8a becomes positive so as to push the shifter dog 6 toward the neutral position. With this construction, however, it takes a certain time until the shifter rod 6 returns to the neutral position. Furthermore, this time is delicately influenced by the coarseness of the dog surface so that the return time is not constant. If the positive angle is made too large, the wear is accelerated by the slip between the shift cam 2 and the push rod 3.
To obviate the first mentioned defect it has been proposed a construction shown in FIG. 6 in which the intermediate portion of the shift rod is constructed to freely contract and expand by interposing a spring 11. According to this improvement, a detent mechanism 12 is engaged with the cam 2 for rapidly moving the shifter dog 6 from the neutral position to the reverse position by the force of spring 11 regardless of the operating speed of the shift rod 1. With this improvement, however, not only the second defect can not be solved but also a problem similar to the second defect occurs. These defects also occur when a rotary cam 2' as shown in FIG. 7 is used instead of the shift cam 2 which is moved linearly.